WALTERD. ALBERTAND FREDW. UPSON
132
[CONTRIBUTION FROM
THE
CHEMICAL LABORATORY, UNIVERSITY
Vol. 57 OF
NEBRASKA 1
The Action of Barium Hydroxide on Certain of the Monobasic Sugar Acids BY WALTERD. ALBERTAND FRED W. UPSON Introduction This paper presents the results of a quantitative study of the decomposition products resulting from the action of barium hydroxide on four sugar acids a t a temperature of 140' for twentyfour hours. The compounds studied were dgluconic, I-arabonic, dl-glyceric and dl-lactic acids. While numerous studies of the action of alkalies on the sugars have been made, there is little work available on the action of alkalies on the sugar acids. It usually has been assumed that acids formed in the degradation of sugars with alkalies are relatively stable under the conditions employed. The experiments recorded in this paper indicate that this assumption is not always justified, particularly when higher concentrations of alkali and temperatures above 100' are employed.
Experimental Materials.-Barium d-gluconate was prepared from commercial calcium d-gluconate. Barium I-arabonate was prepared from calcium I-arabonate made from l-arabinose by oxidation with bromine in the presence of calcium carbonate. Barium dl-glycerate was prepared from calcium dl-glycerate made from glycerol according to the method of Debus.' The purity of the salts was established by means of barium determinations. The dl-lactic acid was prepared from pure zinc lactate by precipitation of the zinc ion as the sulfide and extraction of the lactic acid from the filtrate with ether. The concentration of the aqueous solution was determined by titrating weighed portions with standard sodium hydroxide solution. Procedure.-One-half equivalent of the barium salt was placed in a 500-ml. round-bottomed flask with one and one-half equivalents of barium hydroxide which had been dissolved in hot water and filtered. The solution in the flask was made up to 500 ml., the solution boiled and a rubber stopper wired in place. The stoppered flask was partially immersed in water in a cast iron bomb which was heated in a n oil-bath by an electric hot-plate. The temperature within, which was indicated by the reading of a pressure gage on the bomb, was held at 140' for twenty-four hours. After this heating period the reaction mixture was treated as outlined below. A solid residue consisting of barium carbonate and barium oxalate was filtered out of the slightly colored solution. Some additional barium oxalate usually precipitated when the solution was diluted t o 1500 ml. and heated. The solids were dissolved in hydrochloric acid. (1) Debus Ann., 106, 79 (1868).
Calcium oxalate was precipitated and reprecipitated from solution in the usual manner, and dried in air to constant weight. After the solid residue had been taken out, the barium ion was removed from the filtrate with sulfuric acid until only a trace of barium remained. The free organic acids were then separated into a volatile and a non-volatile fraction by distillation in vacuo from a water-bath at 60". Two 50-ml. portions of water were added, each of which was distilled to dryness. The total acidity and the acidity due to formic acid were determined by the method of Evans and Hass* on aliquot portions. The remaining part of the volatile acids was neutralized with sodium hydroxide and evaporated t o dryness. Upon distillation with sulfuric acid the dry sodium salts from gluconic, arabonic and glyceric acids each yielded acetic acid, as determined by the Duclaux constants and the derivative formed with p-toluidine. Acetic acid was not found among the decomposition products of lactic acid. The non-volatile acids were dissolved in water and separated into two portions by extraction with ether for fortyeight hours.8 The extract was converted to the zinc salts and the zinc lactate removed as completely as possible. Its purity was determined frequently by igniting samples well dried in air and weighing the zinc oxide. The gummy residue remaining after the removal of zinc lactate was converted into brucine salts which were recrystallized until substances having constant melting points were obtained. An unidentified salt which darkened at 192' before melting a t 197-199' was obtained from arabonic acid, From gluconic acid small amounts of salts melting at 186-188" and 221 'were obtained. The former may be the brucine salt of 1,3-dihydroxybutyric acid, and the latter that of dl-glyceric acid. The amounts were too small for certain identification. From the portion of non-volatile acids not soluble in ether a small amount of a very insoluble calcium salt was obtained which has been identified as calcium meso-a&dihydroxyadipate. Anal. Calcd. for CaCsHgOs: Ca, 18.54. Found: Ca, 18.39. The free acid obtained from the calcium salt melted a t 172" (corr.) after being recrystallized once from ethyl acetate and twice from glacial acetic acid. The acid was found to be optically inactive. Anal. Calcd. for C&OOS: C, 40.43; H, 5.66. Found: C, 40.77; H, 5.89. A sample of pure phenylhydrazide prepared from the acid melted at 215" (corr.). This is a new compound. Anal. Calcd. for C I ~ H B N ~ O C, ~ : 60.30; H, 6.19. Found: C, 60.32, 60.34; H, 6.69,6.73. For the purpose of identification some mew-ad-dihy(2) Evans and Hass, THISJOURNAL, 48,2703 (1926). (3) Evans, Edgar and Hoff, ibid., 48, 2666 (1926).
BARIUM HYDROXIDE ON MONOBASIC SUGAR ACIDS
Jan., 1935
droxyadipic acid was prepared according to the method of Le Sueur.* It melted at 172” (corr.) and melting points of mixtures were unchanged. Some of this acid was converted into the phenylhydrazide which melted at 215.5’ (corr.). Melting points of several mixtures of this phenylhydrazide with that obtained above were also 215”. The acid was thus identified as meso-a,a’-dihydroxyadipicacid. Separate portions of the barium salts one twenty-fifth as large as those used above, were heated in 25 X 100 mm. stoppered Pyrex test-tubes for the carbon dioxide determinations. An apparatus described by Clowes and Coleman6was modified slightly for the determinations.
COOH
I H-C-OH I HO-C-H I H-C-OH I H-C-OH I
7
HO--C-OH C-OH II
I I H-C-OH I
HO-C-H
CHzOH &Gluconic acid
CH20H 1,2-Enediol H HO-C-OH
I I1 HO-C I
Formic
3.28 1.92 8.93 0.17
1.97 6.36 3.20 0.53
Oxalic
Lactic Carbonic Total
1.49 5.7 4.0
65.2 59.9 65.2 98.2
..
1.92 2.58 5.09
..
73.9 76.5 86.4 98.9
(4) LeSueur, J . Chem. Soc., 93, 716 (1908). (5) Clowes and Coleman, “Quantitative Chemical Analysis,” P. P. Blakiston’s Son and Co., Philadelphia, 1914, p. 103. (6) Fischer, Ber.. 48, 1145 (1895);Wohl and Neuberg, {bid., 33, 3095 (1900), Nef. Ann., 403, 205 (1914); Glattfeld, A m Chem J . . 50, 137 (1913). (7) Evans and Conaway, THISJOURNAL, 54,3680 (1930).
7
C-OH
I H-C-OH I
I I
H-C-OH
CHzOH 2,3-Enediol
CHnOH 3,4-Enediol
H COOH H-L-OH
I I The main constituent of the “other volatile HO-C-H acids” is acetic acid from all starting substances I
except lactic acid. Traces of lactic acid were present in every distillate since it is somewhat volatile. Traces of unchanged gluconic and arabonic acids were isolated as the phenylhydrazides from the original reaction mixture. Since barium hydroxide is not an oxidizing or a reducing agent, some product must be oxidation products if others are reduction products of the sugar acid molecule. It is evident from the empirical formulas that lactic and acetic acids are reduction products while formic, oxalic and carbonic acids are oxidation products of glyceric, arabonic and gluconic acids. When the theory of enediol formation6 as developed from studies of the action of alkalies on the sugars, is applied to the sugar acids, the following possibilities may be presented. Evans and Conaway’ state that it is generally accepted that pyruvic aldehyde formation is the forerunner of lactic acid in the alkaline decomposition of sugars. The formation of lactic acid from the active form of glyceric aldehyde resulting from the action
I I HO-C II
CHOH
J
H-C-OH
TABLE I CARBONRETURNED IN PERCENTAGE OF TOTAL CARBON Acid
H HO-C-OH
C-OH
With very few exceptions the figures presented below are averages of three to six or more determinations.
Gluconic Arabonic Glyceric Lactic
A 7
H-C-OH
Discussion of Results
Other volatile
133
HO-C-H
7
CHaOH I-Arabonic acid
HO-C-OH C-OH II
I I
HO-C-H
A 7
HO-C-H
I
CHiOH 1,2-Enediol
COOH
I CHOH I
HO-C-OH C-OH I
I/ I HO-C-H I HO-C
CHzOH 2,3-Enediol
HO-C-OH
I1
C-OH
e
CHzOH dl-Glyceric acid
I
CHZOH 1,a-Enediol
of alkali on gluconic and arabonic acids may be explained by a mechanism presented by Evans and H a s 2 Its formation from glyceric acid may be explained if we suppose that glyceric acid is reduced first to glyceric aldehyde. Such a reduction is entirely possible since combustible gases which contain hydrogen as one constituent were formed in small amounts in all experiments of this type. The second Ca fission product of gluconic acid resulting from the breaking of the 3,4enediol must also be capable of yielding lactic acid since approximately 65% of the carbon of this acid is returned as lactic acid. This breaking product is tartronic aldehyde, which may be converted to glyceric aldehyde upon reduction. Since nearly 60% of the carbon of arabonic acid is returned as lactic acid and since no acetic acid is obtained from lactic acid, acetic acid must come from Cz residues and not from the oxidation of pyruvic aldehyde, pyruvic acid or lactic acid. Its formation from the CZ fission product of gly-
134
WALTER
n.ALBERTAND FREDw. UPSON
ceric acid may be explained by a mechanism recently advanced by Evans and Hockett.* The CZ fission product from gluconic and arabonic acids, unlike that from glyceric acid, would rearrange to form glyoxal. As is well known, alkalies convert glyoxal into glycolic acid even a t 20". The formation of acetic acid from glycolic acid may be explained by the method of Evans and Hockett if we suppose that the glycolic acid is first reduced to glycolic aldehyde. Oxalic acid may arise from the oxidation of any CZfission product. Formic acid must arise directly from the rearrangement of dihydroxymethylene, a fission product of 1,2 enediols.
VOl. 57
TABLE I1 PERCENTAGE OF CARBON RETURNED IN TERMS OF TOTAL CARBON FROM SUGARAND SUGARACIDS Acid. .
. . . .Formic
&Glucose d-Gluconic acid 2-Arabinose 1-Arabonic acid &Glyceric ald. &Glyceric acid
Acetic
Oxalic
0.29
0.68
..
24.5
..
25.5
3.28 1.63
1.97 0.80
1.49
65.2 10.8
1.92
.
..
73.9 13.2
1.92
6.36
5.7
59.5
2.58
76.5
1.1
1.4
..
35.0
..
37.5
8.93
3.20
4.0
65.2
5.09
86.4
.
Lactic Carbonic Total
Since Evans used lower temperatures, it seemed of interest to find the effect of 3 N barium hydroxide on glucose a t 140'. Accordingly, one experiHO-C-OH + HCOOH I/ ment was carried out with this end in view. The oxidation of dihydroxymethylene will acOne-half mole of anhydrous d-glucose was count for carbon dioxide. treated in exactly the same manner as the barium salt of the acid had been treated. No oxalic acid HO-C-OH 0 +COz + H2O li was found and no determination of carbon dioxide The formation of meso-a,a'-dihydroxyadipic was made. The amounts of the carbon accounted acid from gluconic acid may be explained by for as formic, acetic and lactic acids were 8.8, means of a double mechanism of the type leading 5.0 and 29.8%, respectively. These values are to the formation of metasaccharinic acids. The considerably higher than those obtained by Evans mechanism presented by Evans, Edgar and Hoff3 at 50' and values for formic and acetic acids are will apply readily to the transformation if one as- also higher than those obtained with gluconic sumes that an aldehyde group is first formed at acid. This indicates that the higher temperature each end of the molecule by the reduction of the favors the formation of the volatile acids in the carboxyl group and the oxidation of the primary action of alkalies on the hexoses. The significant difference between the sugars and the sugar acids alcohol group. is OH--C-CHOH-CHOH-CHOH-CHOH-CHO + the relatively much higher percentage of lactic acid obtained from the latter. HOOC-CHOH-CH2-CH2-CHOH-COOH
+
The action of barium hydroxide on the sugar acids is somewhat related to the work of Evans and his students on the action of potassium hydroxide on d-glucose, I-arabinose7and dl-glyceric aldehyde2p9the correspondingsugars. The part of the work of Evans which deals with the treatment of the three sugars with 3 N potassium hydroxide a t 50' is summarized in the following table for the purpose of comparing his results with those of the present work. The proportion of carbon accounted for as formic, acetic and lactic acids is much less in every case in the experiments with the hexoses, than with the corresponding acids. While a total of 13.2-37.5% of the carbon is accounted for by Evans and his students, 73.7-86.4% is accounted for in the present work (8) Evans and Hockett, THISJOURNAL, 62,4065 (1930). (9) Evans and Cornthwaite, ibid., 60, 486 (1928).
summary 1. Barium salts of &gluconic, I-arabonic, dlglyceric and dl-lactic acids have been treated with three normal barium hydroxide for twentyfour hours at 140' and the decomposition products have been determined quantitatively. 2. Gluconic, arabonic and glyceric acids are practically completely decomposed into simpler substances while lactic acid is almost unaffected by the treatment. 3. The amounts of the carbon recovered as lactic acid are three-fifths of the total carbon of arabonic acid, almost two-thirds of that of gluconic and glyceric acids, and 98% of that of lactic acid. The proportion of oxalic and acetic acids is greater by far from arabonic acid than from the others. LINCOLN, NEBKASEA
RECEIVED OCTOBER 10, 1934
